Study On Reliability And Trust Of Cyber Physical System For Cooperative Driving

With the development of V2X technology, the ranges of information perception and the variety of information constantly increase; meanwhile, the interactive relationship among vehicles is enhanced with the increasing of road traffic density which enables the cooperative driving using communication and interaction. However, the cooperating performances are influenced by all kinds of multifarious factors. Thus, analyzing and evaluating these factors is the fundamental work to improve the cooperating performances which need more attention and urgent research work.Cooperative driving system is a continuous process which is influenced by discrete information and has the typical characteristics of cyber physical system(CPS). In general, the cooperative driving system can't get the desired performances which is influenced by many factors, such as the V2X(Vehicle to Vehicle and Vehicle to Infrastructure communications) based obtained traffic spatio-temporal information involves the unreliable factors of unsynchronized data, outliers, propagation delay, errors and redundancy, etc., in the process of information collecting, propagating and processing which lead to the information is unreliable, and the inter-vehicle's interaction may be failed due to untrusted behaviors, such as spoofing, denial of services, and so on. These information unreliable factors and untrusted behaviors seriously affect the safety and efficiency of the cooperative driving system. The existing researches of the above information unreliability factors and untrusted interaction behaviors either study using the perspective of cyber system, or study using the perspective of physical system, or study a single factor, whose integrity of the study is poor and lack of comprehensive analysis indicators.Based on above background, this paper takes the reliability analysis as the comprehensive analysis indicator and focuses on the reliability problems of CPS for cooperative driving, this paper provides a new perspective and systematic method for analyzing cyber physical fusion mechanism of cooperative driving and studying the reliability problems of CPS for cooperative driving through designing architecture of CPS and studying the description method of T-CPS; then on this basis, this paper uses the cyber physical deeply fusion as breakthrough point and mainly studies some reliability improving methods and optimal mechanism of information sources, information propagation and information processing in information reliability analysis of CPS for cooperative driving, and studies the trust relationship description, the trustworthiness evaluation among vehicles and the trust delivery mechanism in trusted interaction analysis of CPS for cooperative driving. Our reliability analysis of CPS for cooperative driving can improve the safety and efficiency of cooperative driving physical system through reliable information and trusted interaction in cyber system.Thus, the main results of this study are as follows:(1) Based on the hybrid characteristics of discrete cyber system and continuous physical system interacting and fusing in CPS, a discrete and continuous hybrid CPS architecture is presented which is driven by spatial-temporal event.The proposed architecture describes the main body of the discrete and continuous hybrid CPS, and then define spatio-temporal event-based CPS event and design MAS-based CPS client. Then, the inner cyber physical fusion process of the proposed CPS architecture is analyzed using the different functional CPS client and CPS event driven mechanism. Finally, taking the vehicular velocity regulation and control system for instance, the inherent cyber-physical fusion process of vehicular velocity regulation and control in cooperative driving system is analyzed and formalized with our proposed CPS architecture.(2) Aims at the problems of spatio-temporal hybrid characteristics of T-CPS is difficult to description and there are so many physical entities for abstracting and marking that may lead to the state space explosion problem, an colored spatial-temporal petri nets(CSTPN) is proposed to describe and analyze T-CPS.The proposed T-CPS description method abstract and mark mass traffic entities using colored tokens to solve the state space explosion problem, a colored spatial-temporal petri nets(CSTPN) is designed to describe and analyze T-CPS. Besides, in order to instantiate our CSTPNs modeled T-CPS, a typical T-CPS case which is called traffic intersection coordination control system(TICCS) has been modeled and analyzed. On this basis, the overall framework of reliability analysis of CPS for cooperative driving is proposed and the main work of this paper in the overall framework is discussed.(3) For improving the information reliability of CPS for cooperative driving, an improved vehicle safety state information calculation method, an information propagation reliability enhancement mechanism, an improved SVM based traffic information classification method and an improved firefly algorithm-based spatio-temporal outlier detection mechanism(IFA-STODM) are proposed.Based on V2X technology, The reliable cooperative driving information is obtained through improved vehicle safety distance calculation method with the perspective of cyber physical deeply fusion; for solve the problems of propagation delay, errors and redundancy in the process of information propagation, an information propagation reliability enhancement mechanism is proposed; for classifying the cooperative driving information with the characteristics of multi-source, heterogeneous and hierarchical, an improved SVM based traffic information classification method is presented in the process of traffic information fusion; for solving the problems of data synchronization and the traffic spatio-temporal outlier detection, an improved synchronization operator and IFA-STODM is proposed.(4) For improving the trusted interaction of cooperative driving system, aims at trust relationship description, trustworthiness evaluation and trust delivery related problems of dynamic interaction among vehicles in cooperative driving process, a novel membership cloud model-based trust model is presented, and then an improved trusted computing-based dynamic trust evaluation model and trust delivery mechanism are proposed.Aims at the problems of the existing trust models can not accurately or perfectly describe the trust relationship and its inherent characteristics, this paper proposes an improved membership cloud theory based trust model. For evaluating the trustworthiness and resisting untrusted behaviors among vehicles, a novel trust evaluation model is proposed through introducing the related factors and a trust delivery mechanism is presented through the improved trust chain of the trusted computing theory which provides a new method to verify the entire cooperative driving system.In conclusion, this paper studies some key technologies and problems of overall framework in reliability problems of CPS for cooperative driving; the proposed CPS architecture and the proposed description method of T-CPS provides an a new perspective and systematic method for analyzing cyber physical fusion mechanism of the transportation application system. The research results of information reliability analysis and trusted interaction analysis are expected to provide technical support and guidance for solving key technologies and problems of overall framework in reliability problems of CPS for cooperative driving using the CPS perspective.